Cryogenic propellant depot and integral sunshield

ABSTRACT

A cryogenic propellant depot and sunshield are provided for operation in earth orbit to fuel or refuel other space vehicles. The sunshield is deployed to effectively mitigate solar radiation emanating from the earth and the sun thereby providing a long term storage solution for cryogenic fluids prone to boil-off. The depot has supporting subsystems to include station keeping equipment and communication equipment so that the depot can be independently controlled. Inflatable booms are used to deploy the sunshield in a desired pattern around the depot.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/359,015 filed on Jan. 23, 2009 and is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to cryogenic propellant depots used forthe fueling of space vehicles in earth orbit, other orbits, deep spaceor near celestial bodies, and more particularly, to a cryogenicpropellant depot placed in space having an integral sunshield tooptimize storage of liquid cryogens by shielding the depot from solarradiation.

BACKGROUND OF THE INVENTION

Space exploration is limited by a number of factors that prohibit thedistance to which space vehicles can travel from the earth to the restof the solar system. One obvious limitation is the size of a payloadthat can be placed into earth orbit and beyond. Tremendous power andfuel requirements are required to place larger payloads into earthorbit, and to then project those payloads to other locations in thesolar system, such as the moon or Mars. The proposed NASA Ares-5 rocketis capable of delivering approximately 69 tons to earth escape velocity.However, NASA's current architecture requires a minimum of 77 tons tocomplete a crewed lunar mission that includes travel to and from themoon back to earth. Design changes for existing rockets can be achieved,but not without great additional expense. Increasing the payloadcapacity of existing launch vehicles is required for extended spaceexploration to locations such as Mars missions.

One alternative for satisfying mission performance needs for extendedspace exploration contemplates the use of an on-orbit fueling station,that reduces the Earth to orbit launch vehicle performance requirementsdown to the capability of existing booster rockets, and also enablesgreat flexibility in attending to the different types of space missionsin the expanding space industry. Providing an orbital refueling stationhas been contemplated with some prior designs, such as by NASA andBoeing. These prior designs typically are large space “gas stations”storing both oxidizer (typically LO2) and fuel (typically LH2) requiringon orbit assembly of elements launched by numerous launch vehicles.These large space stations also typically rely on zero-gravity cryofluid management requiring significant additional development. However,a need still exists for providing an orbiting propellant depot usingexisting or near term technology that can be easily integrated withinexisting payload fairings, is economically feasible, and provides areliable design that minimizes potential failure modes based upon theduration of time in which the propellant depot would be operating inspace.

SUMMARY OF THE INVENTION

In accordance with the present invention, a cryogenic propellant depotand integral sunshield are provided that can be launched from within anexisting payload fairing on existing launch vehicles. The depot canreside in low earth orbit, and provides the capability to fuel/refuelmany types of space vehicles. The proposed depot design also supportslocations beyond low Earth orbit such as Earth-Moon Lagrange points, lowlunar orbit, low Mars orbit or the lunar surface and is capable ofsupporting a wide range of space transportation architectures.Preferably, the depot would be launched empty and be fueled byadditional propellant servicing launches.

The depot includes a relatively lightweight, cryogenic tank designed tocontain a single fluid, either an oxidizer such as liquid oxygen, orfuel such as liquid hydrogen. The term “depot” when used alonehereinafter collectively refers to the invention comprising the tank andthe sunshield as an integrated system. The cryogenic tank includes anequipment deck that contains a docking collar allowing the depot toconnect to another space vehicle for transfer of cryogenic liquid. Thedepot would also include integral avionics, control valves fordispensing of the cryogen, station keeping propulsion equipment, andcommunications equipment. The depot may incorporate a propulsion systemin the form of a rocket engine such that the depot itself constitutes anupper stage of the launch vehicle. The upper stage may carry a payload,such as a satellite. Thus the depot in this embodiment comprises threecomponents: the upper stage, the shield, and the payload.

To minimize boil off of the liquid, a low conductivity support truss andthermal isolation gas reservoir is placed between the equipment deck andthe tank. To minimize structural mass and maximize the depot propellantcapacity within payload fairing envelopes, the thermal isolation gasreservoir and cryogenic tank share a common, insulated bulkhead.

The sunshield is stored on or adjacent to the equipment deck. Once thedepot is in orbit, the sunshield is deployed around the cryogenic tankto thereby minimize heating from the sun and earth. The sunshielddeflects radiated heat from these sources to deep space. The sunshieldprovides a passive, structurally reliable, and affordable solution tominimize boil off of the liquid within the tank.

Once the sunshield has been deployed, the entire depot slowly spinsabout its longitudinal axis to provide centrifugal acceleration. Thestation-keeping propulsion system is used to initiate and control thisspin. The centrifugal acceleration provides positive gas/liquidseparation by forcing liquid outward toward the tank sidewall, resultingin a gaseous ullage in the center of the tank. Cryogenic fuel managementwithin the tank is greatly improved as the gaseous core may be moreeffectively vented than a liquid—gas slurry. This venting is similar tothe settled ullage venting of existing cryogenic upper stages.Centrifugal settling also simplifies propellant acquisition andtransfer, thereby avoiding the need for additional liquid acquisitiondevices that would otherwise be required to separate gas and liquidprior to liquid transfer. Propellant transfer into and out of the depotis accomplished by differential pressure between the tank and thereceiving vehicle/tank; very similar to the manner in which launchvehicle engines are fueled on existing cryogenic stages.

The well insulated depot, by incorporation of the sunshield, thethermo-isolation gas reservoir, tank geometry and other heat reductionmeasures enables the depot to stop rotating for docking operationswithout concerns regarding excessive gas and liquid heating thatotherwise might be a concern for a tank that was subject to increasedboil-off because of its exposure to solar and earth heating.

Vented gas from the tank can be stored in the thermal isolation gasreservoir located at the front of the tank, or can be vented to vacuum.During quiescent operation, the reservoir is preferably maintained atjust below tank pressure to ensure flow of boil-off gas from the tank tothe gas reservoir. The reservoir serves as the last heat sink betweenthe equipment deck and the tank. This reservoir also supplies gas forthe reaction control system used to control the depot's attitude andposition as well as positive pressure expulsion of liquids duringpropellant transfer.

The sunshield is an assembly comprising a plurality of sunshield panelsor petals, arranged in pairs and deployed by pneumatic inflation devicesor other method of linear actuation by inflation that extend the pairsof panels in a pre-designated configuration. Each of the sunshieldelements/petals may have multiple layers of materials. When thesunshield is deployed, it forms a truncated cone-shape in which the endof the tank opposite the equipment deck remains exposed to deep space.When the sunshield is fully deployed, it conceals the tank when viewingthe tank from the front (equipment deck) or side (a direction orthogonalto the longitudinal axis of the tank). When the depot is in orbit, theend of the depot with the equipment deck and docking port maintains anorth or south ecliptic orientation that allows the sunshield to mosteffectively protect the tank from both the sun's and earth's radiation.The shield layers can be configured at slightly spaced angles to provideopen passages to better direct thermal energy out to deep space and awayfrom the propellant tank. Thus, radiation energy passing through anygiven sun shield layer will be preferentially directed down, toward thesun shield open end and out to deep space rather than being trapped andeventually heating the liquid cryogen.

By the robust design of the present cryogenic depot and integralsunshield, inter-planetary space missions are no longer limited bylaunch vehicle performance. Smaller, less costly launch vehicles can beused, and space explorations can be extended much farther into the solarsystem. The depot of the present invention enables near termimplementation to support the diverse needs in the space industry,thereby reducing costs for all aspects of space utilization. Otherfeatures and advantages of the present invention will become moreapparent from a review of the following detailed description, taken inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of the cryogenic depot andintegral sunshield of the present invention in a first generalembodiment;

FIG. 2 is a fragmentary perspective view of the cryogenic depot andintegral sunshield of the present invention in another embodimentincluding a segmented shield with individually deployable shield orpanel segments;

FIG. 3 is a simplified cross-section of the depot illustrating liquidgas separation within the tank, and the thermal isolation gas reservoirlocated between the forward bulkhead and the tank;

FIG. 4 is a fragmentary perspective view of the sunshield deploymentassemblies as attached to the equipment deck and housed within thefairing of the launch vehicle during launch;

FIG. 5 is an elevation view of one of the sunshield assemblies asstowed;

FIG. 6 is a simplified fragmentary perspective view illustrating adispensing roller of a sunshield assembly after a sunshield panel hasbeen deployed;

FIG. 7 is a cross-section of a dispensing roller and mounting brackets;

FIG. 8 is a cross-section of an inflatable linear actuator that houses amain boom prior to deployment of the panels;

FIG. 9 is another cross-sectional view showing a sleeve covering theinflatable linear actuator to hold the main boom prior to deployment ofthe boom;

FIG. 10 is a perspective view of the sleeve that covers the inflatablelinear actuator;

FIG. 11 is an exploded elevation view of components of the T-boom orcross boom assembly;

FIG. 12 is a perspective view of a cradle that houses the cross boomprior to deployment of the cross boom and the manner in which the crossboom is packed in the cradle;

FIG. 13 is a perspective view illustrating the cross boom stowed withinthe cradle;

FIG. 14 is a simplified schematic perspective view of the sunshield asit begins to deploy by lengthening of the main boom;

FIG. 15 is another simplified schematic perspective view of thesunshield when the main booms are fully deployed;

FIG. 16 is another simplified schematic perspective view showing thesunshield fully deployed by extension of the cross booms that laterallydisplaces the sunshield panels thereby closing the gaps between thepanels;

FIG. 17 is a perspective view of the depot of the present invention asit prepares to dock with another space vehicle;

FIG. 18 is another perspective view of another embodiment wherein thedepot comprises the upper stage of a launch vehicle with a propulsionsystem that carries a payload such as a satellite; and

FIG. 19 is a schematic view of the depot in earth orbit such that thedepot maintains a north ecliptic orientation to minimize exposure of thedepot to solar and earth heating;

DETAILED DESCRIPTION

In accordance with the present invention and in one aspect of theinvention, it includes a combination of a cryogenic propellant tank andan integral sunshield. According to this first aspect, the propellanttank can be incorporated as the upper stage of a launch vehicle furtherincluding a propulsion system that can carry a payload such as asatellite. In another aspect of the invention as a subcombination, itmay be considered a sunshield especially adapted for space vehicles. Inyet another aspect of the invention as a subcombination, it may beconsidered a cryogenic propellant tank placed in orbit and especiallyadapted for fueling and refueling space vehicles. In another aspect ofthe invention, a method is provided for deploying a sunshield for aspace vehicle. In yet another aspect of the invention, a method isprovided for providing a readily accessible liquid within a cryogenictank while in earth orbit for transfer to another space vehicle.

FIG. 1 illustrates a first embodiment of the present invention includinga cryogenic propellant depot and integral sunshield system 10. Asunshield 12 is secured to a cryogenic tank 14 that is placed into earthorbit by a launch vehicle (not shown). The sunshield 12 surrounds thetank to form a truncated cone shape. The sunshield is secured to thetank adjacent an equipment deck 24, and the sunshield extends beyond alength of the tank in a diverging fashion thus forming the cone shape.The sunshield 12 can have multiple layers of reflective material 13 toprovide optimum protection to the tank 14. The shield is shown brokenaway in FIG. 1 to illustrate the covered tank 14. The open end of thesunshield provides a view factor to deep space allowing re-radiation ofenergy to the cold of deep space from the sun shield and tank.

FIGS. 2 and 3 illustrate another preferred embodiment of the cryogenicpropellant depot and integral sunshield system 10 of the presentinvention. In this embodiment, the sunshield 12 comprises a plurality ofsegments in the form of reflective panels or petals 30 that surround thetank 14 such that the panels when deployed form a truncated cone aroundthe tank. In FIG. 2, a few of the panels have also been removed in orderto illustrate the tank 14 in its general orientation with the sunshield.Each of the panels is individually deployable, as set forth in moredetail below.

The tank 14 preferably has a cylindrical sidewall 16, and is sized inlength and circumference to fit within a designated payload fairing orlaunch vehicle outer mould line. Preferably, the tank is very thinwalled which provides minimum structural mass, thermal mass and thermalconductivity to the rest of the depot. A docking port 22 is disposed atone end of the tank, along with the equipment deck 24 and at least onesolar panel 20 that is used to provide power to the equipment deck 24.The equipment deck supports the avionics and other conventional(?)mechanical/electronic equipment (not shown) used to control functioningof the depot. More specifically, the equipment deck may support avionicsthat are used to navigate the depot, communications equipment allowingthe depot to be controlled by radio communications with the earth, andcontrol valve assemblies that are used to control the selective transferof liquid from the tank to the docking port and gas transfer for tankpressure control. The equipment deck may further support conventionalstation-keeping equipment (not shown) that is used to maintain the depotin a desired orbit and orientation, as well as to provide rotation ofthe depot about its longitudinal axis. The station-keeping equipment mayinclude a series of small propulsion jets that are spaced around aperiphery of the equipment deck, and which are selectively fired topropel the depot, and to impart a desired spin about the longitudinalaxis of the depot. These jets can use gas from the reservoir forreaction mass.

Referring to FIG. 3, a simplified schematic diagram is provided of across section of the tank and sunshield. The sunshield panels 30 extendaway from the tank 14 at a desired angle A with respect to thelongitudinal axis X-X of the tank. The propellant tank 14 has thesidewall 16 with one end 19 thereof that is covered by an attachedbulkhead 33. A gap or space 34 exists between the end 19 of the tank 14and the interior surface 33 of the bulkhead. This space 34 acts as athermal isolation reservoir that thermally isolates the liquid 36 withinthe tank and helps to prevent heat from being transferred from thecomponents attached to the equipment deck 24, such as the solar panels20, avionics and the docking ring 22. The bulkhead 33 may have anintermediate low conductivity truss support 62 placed between the end ofthe bulkhead 33 and the equipment deck 24. This composite truss support62 further helps to isolate liquid within the tank 16 from heat transferby conduction through the equipment shelf 24.

FIG. 3 also illustrates that the liquid 36 within the tank is forcedconcentrically outward towards the sidewall 16 of the tank, and any gas38 that is within the tank forms a core that extends along thelongitudinal axis x-x of the tank and is centered within the tank. Asmentioned, the station-keeping equipment provides a very slow rotationof the propellant tank about its longitudinal axis that separates theliquid and gas within the tank, and thus creates the gas core. Asnecessary, the gas core 38 may be vented to maintain desired pressureswithin the tank, and can be vented into the thermal isolation reservoir34 or dumped overboard. This relatively cool gas from the reservoir 34also helps to chill the thermal isolation reservoir to further preventheat transfer to the liquid within the tank. Gas from the reservoir canbe further used to vapor cool key parts of the depot to further reduceliquid heating.

FIG. 4 illustrates the sunshield 12 when stowed within the launchvehicle. The sunshield in a preferred embodiment of the presentinvention includes six sunshield assemblies 26 that are disposed asshown around a periphery of the end of the tank. As shown, thearrangement of the assemblies 26 fit within the fairing envelope 40 thatis longitudinally aligned with the upper stage 42 of the launch vehicle.In this figure, the tank is shown disposed within a launch vehiclefairing 42; however as mentioned, the depot can be constructed integralwith the upper stage of a launch vehicle in which case the tank wouldinclude primary propulsion components.

Referring to FIG. 5, details are illustrated of one of the sunshieldassemblies 26. An I-Beam mount 44 secures the assembly 26 to theequipment deck of the depot. The assembly 26 includes a pair ofsunshield panels 30. Each of the panels 30 is stored in a rolledconfiguration about a corresponding roller 52 that extends from theI-Beam mount 44 by roller mounting brackets 54. The panels 30 aredispensed from their corresponding rollers 52 by an inflatable linearactuator device 70 disposed within an inflatable linear actuator sleeve46, as discussed in more detail below with respect to FIGS. 8-10. Theinflatable linear actuator houses an inflatable main boom that isprogressively extended by pneumatic force which in turn causes thepanels to unroll and extend. The distal or free ends of the panels 30are secured to a cross boom or T-Boom 100. As discussed further belowwith respect to FIG. 8, the free end of the main boom 86 connects to anend cap 85. A connecting assembly 48 interconnects the end cap 85 andthe cross boom 100. Once the main boom has fully deployed, then theT-Boom deploys in an orthogonal or transverse direction to laterallyspread the panels 30 to their fully deployed polygon configuration.

Referring to FIGS. 6 and 7, additional details are illustrated withrespect to sunshield assembly 26. FIG. 6 illustrates one of the sunshield panels 30 after it has been fully unrolled from its roller 52. Apair of end platens 56 provides support to opposite lateral edges of thepanel so that as the panel is unrolled, it maintains a linear deploymentpath. As also shown in FIG. 6, the panel 30 may include multiple layersof material depending upon the particular material used for the panel,as well as the shielding requirements for adequately shielding the tank.Examples of types of material that can be used for the panels includedouble aluminized Mylar® (DAM), double goldized Kapton® (DGK) or glasscloth—vacuum deposited gold (VDG). These materials have excellentreflective properties to effectively deflect radiation away from thesunshield in a directed pattern to deep space. Referring to FIG. 7, itis shown that the roller 52 extends between the roller mounting brackets54, the platens 56 being spaced from the brackets 54, and each end ofthe roller 52 having an extension 60 that is received within acorresponding spherical bearing 58.

Referring to FIGS. 8-10, the inflatable linear actuator 70 is shownalong with the inflatable linear actuator sleeve 46 that covers theinflatable linear actuator. The inflatable linear actuator 70 houses themain boom 86 that is deployed to extend the pair of panels. The boom 86is a flexible, gas impervious cylindrical member made of a materialsuitable for the space environment, such as PBI/Kevlar® with siliconecoating. The main boom 86 is stowed in one or more (3 depicted)longitudinally spaced folded sections. Each of the sections is accordionfolded in a concentric pattern so that as the boom is inflated, theoutermost concentric folded layer is pulled away from the otherconcentric layers. The inflatable linear actuator device includes a rod76, a base support 72 connected to the rod at one end, and a deploymentguide disc 82 disposed at the other end. The boom 86 is held between thebase support 72, disc 82 and the sleeve 46. A central aperture orpassageway 78 extends through the rod. A port 74 communicating with theaperture 78 receives a source of compressed gas. This gas can beobtained from gas within the thermal isolation reservoir 34, or adedicated gas source. The chamber 84 within the disc 82 receives theflow of gas through the aperture 78. End cap 85 is positioned beyond thedistal end of the disc 84. The distal or free end 87 of the boom 86extends over the disc 84 and is sealed to the end cap 85 so that whencompressed air begins to fill the chamber 84, the end cap progressivelydisplaces away from the inflatable linear actuator and the boom 86 isunfurled from its accordion folds. The distal folded section closest tothe end cap 85 unfurls first, followed by the intermediate foldedsection, and then the proximal folded section unfurls. When fullyinflated, the boom extends linearly away from the inflatable linearactuator 70 and in the direction in which the disc 82 is oriented. Thedisc 82 has a cylindrical shaped sidewall that orients the direction ofboom displacement. FIG. 8 also shows an intermediate compressibleelement or gland 80 having a ring shape made of a flexible material suchas Teflon. The gland 80 is compressed or loosened by a set screw toplace a desired amount of pressure upon the interior surface of the boom86 as the boom is inflated. The pressure placed by this intermediategland assists in controlling the boom pressure and hence the speed ofdeployment of the boom. The multiple separate accordion folded sectionsare provided in order to more conveniently configure the boom forstorage, and also to help overcome any additional frictional resistancethat could otherwise be associated with the boom if it were stored in asingle accordion fold. FIG. 10 illustrates the inflatable linearactuator sleeve 46 that extends concentrically over the packed mainboom. As shown, the inflatable linear actuator sleeve may include twohalf sections 90 secured to one another by a pair of securing bands 92and locks 94. As shown in FIG. 9, the installed sleeve 46 encloses theboom 86, but the end cap 85 remains exposed. The inflatable linearactuator sleeve protects the inflatable linear actuator and boom duringtransport and launch as well as ensuring a consistent boom pressure fromthe compressible gland 80 to ensure consistent deployment.

FIG. 11 illustrates the T-boom or cross boom cradle assembly 100. Thecross boom cradle assembly 100 holds the cross boom 102, as illustratedin FIGS. 12 and 13. The cross boom is used to laterally expand thepanels 30 to their fully deployed positions. FIG. 11 also illustratessome of the components of the connecting assembly 48 that interconnectsthe end cap 85 to the cross boom 100. Large bolts 112 attach brackets104 to the end cap 85. The opposite ends of the brackets 104 attach to asurface of the cradle holder 108. Tube sections 114 enable gas to flowthrough the end cap 85 and into the cross boom for inflation of thecross boom. A rupture disc holder 116 receives a rupture disc 118 placedin the fluid path of the tube section 114. When the main boom isinflated, continued pressurization of the main boom will cause therupture disc to rupture at a desired pressure, thereby enabling gas toflow into the cross boom for subsequent inflation of the cross boom. Acheck valve 120 is provided to prevent backflow of gas into the mainboom once the main boom has been pressurized to a desired level. Thepanels 30 are attached to the cross boom assembly by D-rings 101 thatare secured to the cross boom 102. The D-rings 101 are spaced along thewidths of the panels 30 and attach to the free distal ends of thepanels. The D-rings 101 hereby distribute the load of the panels evenlyacross the cross boom. It is noted in FIG. 11 that the gap between thepanels 30 has been exaggerated in order to better illustrate thecomponents of the assembly 48.

Referring to FIGS. 12 and 13, cradle 106 includes a half-cylinder shapedholder 108 and a plurality of flexible retaining straps 110 secured tothe holder 108. The cross boom 102 is stowed in the cradle 106, andstraps 110 hold the boom within the cradle. The straps may use hook andpile material to connect separate sections of strap material together orto connect the straps to the holder 108. The straps may be made from aresilient nylon material. The cross boom 102 is accordion folded withmultiple sets of folds (two depicted), on each end. As gas enters thecross boom, straps sections 110 will separate from one another or thestraps 110 will disconnect from the holder 108 by the pressure of theinflating boom 102. The boom continues to inflate and laterally extendsthe attached panels 30 to their fully deployed position. The independentpanels can remain disconnected or be joined after deployment to provideimproved structural integrity.

Referring to FIGS. 14-16, the sunshield is illustrated in a sequence ofdeployment stages. Other components of the propellant depot have beenomitted in these figures in order for clarity. In FIG. 14, the mainbooms 86 begin to deploy as gas is introduced through the respectiveinflatable linear actuators. The main booms 86 progressively unfurl fromtheir accordion folded configurations. The dispensing rollers rotate tosimultaneously unroll the panels 30 since the distal ends of the panels30 are connected to the T-booms 102.

FIG. 15 illustrates the main booms 86 being fully deployed therebyextending the booms to their full length in a first direction. Thepanels also extend at the desired angle away from the longitudinal axisof the depot to thereby form the generally truncated cone shape.Depending upon the size and shape of the tank to be protected by thesunshield, as well as the particular orbit of the depot in space, theangled orientation of the sunshield can be modified to optimizeradiation shielding. This orientation can be set prior to launch.

Referring to FIG. 16, the cross booms 102 inflate to expand the panels30 in a lateral or transverse second direction to fill thelongitudinally oriented gaps between facing panels 30 of adjacentassemblies 26. Since the booms are deployed in a near zero gravityenvironment, the booms will maintain their cone shaped orientationwithout the requirement of additional support.

Referring to FIG. 17, the propellant depot 10 of the present inventionis illustrated along with another space vehicle 130, which could beanother propellant depot, a propellant delivery vehicle, or a spacevehicle that requires fueling/refueling. The respective docking ports ofthe vehicles are oriented for docking and once docking is achieved, thedesired cryogenic fluid transfer operation would take place. Docking isachieved without having to move or shift the sunshield or the solarpanels. As shown, the sunshield 12 and solar panels 20 do not block thedocking ports thus accommodating docking without further componentmanipulation.

FIG. 18 illustrates another embodiment of the present invention whereinthe cryogenic propellant depot is incorporated as the upper stage of alaunch vehicle in which a propulsion system is used to selectivelypropel a payload in orbit. A pair of rocket engines 190 is shown asbeing secured to the exposed end of the tank 16. These rocket enginesare fueled from the tank and are designed to handle propulsion for adesignated payload. The example payload is shown in FIG. 18 as asatellite 200 that is secured to the docking ring or port 22. Theorientation of the sunshield 12 is the same as in the prior embodiment.

FIG. 19 illustrates the depot of the present invention and its northfacing elliptical orientation with respect to the earth in a low Earthorbit. As shown, this north orientation helps to prevent heat transferto the depot by ensuring continuous shielding of the tank from both thesun and Earth. Placement of the depot in deep space, such as at aLagrange point, where the only significant radiation source is the sun,will benefit from a significantly truncated shield cone with the dockingport directed at the sun.

As provided herein, the sunshield of the present invention is integratedwith a propellant depot wherein the depot can be used to re-fuel otherspace vehicles or other propellant depots. The sunshield of the presentinvention can also be integrated with other configurations such as suchas a launch vehicle upper stage carrying a payload. It shall beunderstood that the sunshield of the present invention is also adaptableto protect other space vehicles and components to include in-spacepropulsion stages, solar or nuclear thermal propulsion stages, or lunarlanders. Because of the relatively simple manner in which the sunshieldgroups can be attached to a structure such as by the I-Beam mounts, thesunshield assemblies 26 can be selectively placed around a space vehicleto cover space vehicles having differing sizes, shapes and functions.Although a cone shape provides an effective sunshield for a cylindricaltank, the inflatable linear actuators can be oriented so that the panelscan be deployed at other angles to best envelop or shield the desiredportion(s) of a particular space vehicle.

Although the present invention has been described with respect to thecombination of a sunshield and a propellant tank or an upper stage, itis also evident that the sunshield and the tank have separate utility assub-combinations and therefore, can be considered distinct inventionsapart from the combination.

In accordance with one method of the present invention, deployment of asunshield is achieved to shield a space vehicle from solar and earthradiation. In accordance with the method, the sun shield is stowed inpairs of sunshield panels. A main boom and T-boom are used to deploy thesunshield panel pairs. The final shape of the sunshield is a truncatedcone that extends over the length of the tank. The tank is fullyenclosed within the sunshield when viewing the depot from the side or anorthogonal direction to the longitudinal axis of the tank.

In accordance with another method of the present invention, a liquidcryogen is made available in earth orbit for transfer to a spacevehicle. The liquid is contained within a tank that spins about itlongitudinal axis. Gas in the tank is maintained in a core that extendsthrough the center of the tank by centrifugal force generated by thespinning tank. Liquid is readily removed from the tank and does notrequire a separate liquid/gas separation procedure prior to transfer tothe receiving space vehicle since the liquid can be tapped from the tankto avoid ingestion of gas. The tank is maintained at an optimaltemperature range with minimal boil-off, thus the tank can cease itsspinning motion during docking without compromising an efficient cryogenstorage that otherwise might be hampered by excessive boil-off occurringduring the transfer.

The use of radial settling for liquid transfer avoids development ofpropellant management devices (PMD). PMDs take advantage of a liquidssurface tension to draw gas free liquid into a tank outlet for fluidtransfer and are used extensively for non-cryogen propellant spaceapplications. The extremely low surface tension of cryogenic propellantsmakes use of PMDs extremely challenging and problematic. Radial settlingalso allows simple, positive measurement of the volume of propellant onthe depot, a serious challenge in a pure zero-G environment.

There are a number of clear advantages to the propellant depot andintegral sunshield of the present invention. Interplanetary spacemissions are no longer limited by launch vehicle performance. Spacevehicles can be fueled and refueled by the propellant depot therebygreatly reducing booster requirements for launch vehicles. The sunshieldprovides an effective and reliable solution to prevent gas boil offwithin the liquid tank, thereby greatly easing cryogen storageoperations. The depot of the present invention is a self-contained, andindependently operable system in which liquid transfer can take placedirectly with a space vehicle without the need for additional equipmentor systems to facilitate the transfer. The tank can be launched empty,which thereby minimizes launch vehicle requirements and eliminates theneed for the depot to support cryogenic operations in Earth'satmosphere. The entire propellant depot and an integral sunshield may belaunched on a single expendable launch vehicle using a medium classrocket, avoiding complicated and costly on orbit assembly. The equipmentdeck that houses the avionics, power generation, valves, andcommunication system is isolated from the cryo fluids thereby enablingthe equipment deck to operate in a more hospitable environment, whilethe cryogenic liquid can be maintained at the requisite temperaturerange. The deployable sunshield mitigates solar and earth radiation heatsources. The open end of the cone allows re-radiation of the energy tothe cold of deep space. The propellant depot and integral sunshield arefully assembled at launch, thereby eliminating any orbital assemblyrequirements.

While the present invention has been set forth with respect to apreferred embodiment for the system, and various structural details forcomponents and sub-combinations, it shall be understood that variousother changes and modifications to the invention can be madecommensurate with the scope of the claims appended hereto.

1. In combination, a cryogenic propellant depot incorporating anintegral sunshield, said combination comprising: a tank having asidewall enclosing a quantity of cryogenic liquid therein; a bulkheadattached to an end of said tank, said bulkhead having an interior openspace defining a thermal isolation reservoir between the tank and thebulkhead; a docking port formed on said bulkhead and communicating withan interior of said tank for selectively evacuating liquid in said tank;and a sunshield attached to said tank, said sunshield having a firstsmaller end secured adjacent said docking port, and a second larger endextending away from said first end and having a length that exceeds alength of said tank, said sunshield forming a truncated cone shape tocover said tank when viewing said tank from a side view; and whereinsaid tank has a longitudinal axis, and said tank rotates about itslongitudinal axis such that a gas core is formed extending through acenter of the tank and along said longitudinal axis.
 2. The combination,as claimed in claim 1, wherein: said sunshield extends symmetricallywith respect to said longitudinal axis in the truncated cone shape. 3.The combination, as claimed in claim 1, wherein: said tank is maintainedat a first pressure, and said thermal isolation reservoir is maintainedat a second lower pressure.
 4. The combination, as claimed in claim 1,wherein: said thermal isolation reservoir includes gas dispersedtherein, said gas being provided from a gas annulus from said tank. 5.The combination, as claimed in claim 1, wherein: said sunshield includesa plurality of layers of materials secured to one another.
 6. A methodof providing solar radiation shielding for a space vehicle having acryogenic propellant depot, the method comprising: providing a sunshieldsecured to said depot, said sunshield comprising a first smaller endsecured adjacent a docking port of the depot, and a second larger endextending away from said first end and having a length that exceeds alength of said depot when the sunshield is deployed, said sunshieldforming a truncated cone shape; and deploying the sunshieldsymmetrically along a longitudinal axis forming the substantiallytruncated cone shape surrounding said depot; and rotating said cryogenicpropellant depot about a longitudinal axis of said cryogenic propellantdepot such that a gas core is formed extending through a center of thecryogenic propellant depot and along said longitudinal axis.
 7. Incombination, an upper stage of a launch vehicle including an integralsunshield, said combination comprising: an upper stage of the launchvehicle including a tank having a sidewall enclosing a quantity ofcryogen liquid therein; a propulsion system incorporated with said upperstage including at least one rocket engine for propelling said upperstage; a bulkhead attached to an end of said tank, said bulkhead havingan interior open space defining a thermal isolation reservoir betweenthe tank and the bulkhead; a docking port formed on said bulkhead andcommunicating with an interior of said tank for selectively evacuatingliquid in said tank; and a sunshield attached to said tank, saidsunshield forming a truncated cone shape around said upper stage andextending beyond a length of said upper stage wherein said tank extendsalong a longitudinal axis of said tank, and said sunshield is deployedsymmetrically along said longitudinal axis in said truncated cone shape;and wherein said tank rotates about its longitudinal axis such that agas core is formed extending through a center of the tank and along saidlongitudinal axis.
 8. The combination, as claimed in claim 7, wherein:said sunshield covers said tank when viewing said tank at a directionorthogonal to said longitudinal axis.
 9. The combination, as claimed inclaim 7, further including: a payload secured to said docking port. 10.In sub-combination, a cryogenic storage tank for a launch vehicle,comprising: a tank having a sidewall enclosing a quantity of cryogenliquid therein; a bulkhead attached to an end of said tank, saidbulkhead having an interior open space defining a thermal isolationreservoir between the tank and the bulkhead; a docking port formedadjacent said bulkhead and communicating with an interior of said tankfor selectively evacuating liquid in said tank; and an equipment deckattached to said bulkhead via a low conductivity truss structure; andwherein said tank has a longitudinal axis, and said tank rotates aboutits longitudinal axis such that a gas core is formed extending through acenter of the tank and along said longitudinal axis.
 11. A method ofmaintaining a liquid cryogen in space for transfer to a space vehiclecomprising: providing a tank containing a quantity of liquid cryogentherein; providing a bulkhead secured to the tank and the bulkheaddefining a thermal isolation chamber; spinning the tank about itslongitudinal axis to create a gas core for gas in the tank that hasboiled; venting gas from the tank into the chamber; removing liquid fromthe tank without interference from the gas core and transferring theliquid to the space vehicle docked with the tank using the gas in thechamber to facilitate transfer of liquid from the tank; and maintainingthe gas in the chamber at a pressure less than a pressure in the tank.